This proposal is to request support for a Keystone Symposia meeting entitled Stem Cell Differentiation and Dedifferentiation, organized by Shinya Yamanaka and Fiona M. Watt, which will be held in Keystone, Colorado from February 15 - 20, 2010. Recent progress in induced pluripotent stem (iPS) cells has shown that stem cells can be generated from differentiated progenies by introducing just a few defined factors. In addition, various stem cells have been isolated from human tissues. Stem cells from patients will provide various tools in understanding disease mechanisms, searching for effective drugs, and evaluating toxicity of drug candidates. Furthermore, human iPS cells and other stem cells may provide various types of cells for regenerative medicine. The Keystone Symposia meeting on Stem Cell Differentiation and Dedifferentiation will critically examine how stem cells, including iPS cells, are isolated, generated and maintained. We will also provide an update on induction of differentiated cells from stem cells. We will also discuss progress in application of pluripotent stem cells and other stem cells in basic research, drug discovery, toxicology, and regenerative medicine.